Okay kiddo, imagine you're playing a very special game with your friend where you both try to trap each other's pieces. This game is called chess.
Now, let's say you and your friend moved some pieces around in the game and then you both realize that you have moved the same pieces to the same positions three times. This means that you and your friend did the same thing three times in a row.
In chess, if you and your friend do the exact same thing three times in a row, it means that you have reached a situation called a "threefold repetition". When this happens, the rules of chess say that the game is over, and it's a tie! It's like saying "we both did the same thing too many times, so let's call it a draw and start a new game".
It's important to remember the threefold repetition rule because it can help you win games by forcing your opponent to make different moves or allowing you to draw a game that you might lose otherwise.